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Silly Autoguiding Question?

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#1 ponz

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Posted 31 January 2013 - 08:45 AM

If the ATLAS and SynScan are supposed to be smart enough to accurately track, provided a proper polar alignment is done; why is there a need for an autoguider?

Ponz

#2 jrcrilly

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Posted 31 January 2013 - 09:28 AM

It's a matter of precision. The mounts track accurately enough for visual use, but imaging requires more - generally less than an arcsecond of error over a period of several minutes. That kind of precision costs much more. Then there is atmospheric refraction, polar alignment error (there's always SOME error), mechanical slop in the mount, optical tube, or in between...

#3 Alex McConahay

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Posted 31 January 2013 - 09:31 AM

>>>> accurately track, provided a proper polar alignment is done; why is there a need for an autoguider?

There is no machine perfect enough to have no mistakes. Those mistakes show as funny looking stars. The autoguider makes corrects for most of the drive trains mistakes before they can show as funny looking stars in your images.

As for why guiding is needed, I remember the story of the Mt. Wilson observatory, where one would expect perfect everything--or at least as perfect as it can get. (I think it is in Lonely Hearts of the Cosmos--Overbye.) It tells of one of the astronomers having to give a kick to the telescope on a regular basis because of a rough spot on the gears.

Alex

#4 CounterWeight

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Posted 31 January 2013 - 10:02 AM

Good to differentiate between the terms tracking and guiding. Your tracking is based up on your setup and alignment, try and get that as good as is reasonable for you. For imaging alignment is somewhat critical.

Autoguiding is something different alltogether. It's there to help iron out the less than ideal in you mechanicals and alignment.

Best results come from giving the guiding 'less work to do', goes back to getting best alignment you can.

Why I think it's better to start with a small scope on a good mount (I did not do this and had 'issues' which helped form my opinion) as it's more forgiving. One thing I don't want to gloss over is that autoguiding can seem a bit of a devil when you start if you need to sdjust the numbers to get it to work. It's plug and play - hope you don't need to go heavy into the play part ;)

There is a lot of help here if that becomes the case.

An easy experiment is to image without guiding and see what you can do as far as sub exposure length and keeping the stars nice and round. Repeat with the guiding turned on (this after you have it dialed in).

Along with digital imaging, and digital procesing techniques - autoguiding is one of the major modern innovations that make this all possible for us amatures.

#5 ponz

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Posted 31 January 2013 - 11:05 AM

You guys have been the best and I'm a member of various forums.

Once the weather clears, I'll take Lucy outside to see what I can do!

Ponz

#6 Alex McConahay

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Posted 31 January 2013 - 11:08 AM

I once heard Tony Hallas explaining that the innovation that did more for our hobby than any other was the ST-4 autoguider. His reasoning, though, was really interesting. It was not that it could guide all that much better. After all, many people could guide manually well enough back then.

However, most chose not to. Let's face it, staring into an eyepiece for 45 minutes clicking up, up. left, right, down....... was a drag, (and 45 minutes was the minimum exposure for one image with EliteChrome). While people would do it for a while to get good pictures, at some point they would say--the heck with this. SO, there were really very few imagers who would do it for more than three or four years before coming to their senses and leaving the hobby. As a result, they never got very good at part two--the processing. However, with the ST-4, people would not be driven away from the hobby. They would get better and better, and learn how to process, and, well, there rest is history. By the way, Tony was telling this story at RTMC sometime in the late 90's, I think. There have been lots more innovations since then, but that gives you some indication of the value of autoguiding.

Alex

#7 ponz

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Posted 31 January 2013 - 06:08 PM

It's been too cold, wet and cloudy here the past few days.

I have another question regarding the guider please.

After aligning the scope as best as possible, do you focus the miniguider on any star or a star within the field of view you wish to photograph?

I don't know how to better phrase that question.

Here's a brief description I found:
http://www.andysshot...autoguider.html

#8 jrcrilly

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Posted 31 January 2013 - 06:53 PM

do you focus the miniguider on any star or a star within the field of view you wish to photograph?


Any star. There's no requirement that the fields even overlap (in off-axis guiding they never will).

#9 ponz

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Posted 31 January 2013 - 07:35 PM

OK, let me see if I understand this correctly.

I align the mount the best I can.
Turn on the autoguider and get any star into focus and the guider calibrates and begins to guide. Guide on what? The star I focused on?

Then what if I want to slew to another DSO to image? Just do it and the miniguider keeps on tickin?

#10 jrcrilly

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Posted 31 January 2013 - 08:03 PM

Then what if I want to slew to another DSO to image? Just do it and the miniguider keeps on tickin?


Depends on your system. You'll have to switch to a new guidestar. Some will automatically do that, some will make you select one yourself. Some will also require you to recalibrate, while others will adjust the guide settings for a change in target declination.

#11 zerro1

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Posted 31 January 2013 - 08:13 PM

With PHD you need to re-calibrate if your sky position changes too drastically. I just open the advanced settings (the brain button) and check the "force calibrate" box each time I change targets.(will automatically calibrate on the first use each time you use it).

You'll likely struggle a bit the first couple uses, but it get's better as you learn.

#12 CounterWeight

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Posted 02 February 2013 - 10:50 AM

One thing worth mention. The Orion miniguider has 3 positioning screws on it. It's not difficult to get the field of the miniguider and the imaging scope (here I'm referring to my f/6 80mm) to overlap. They may take a bit to recognize depending on the exposure length and orietation of each. IMPORTANT - make certain and sure the guidescope is securely tight (with same screws mentioned) if you do this adjustment prior to starting an imaging run(speaking from experience here). Another helpful thing is to dress your cables in a way the provides strain relief, I use Velcro strips I bought at the store and some that came with my mount.






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